This invention relates to numerical techniques for dynamics simulation.
In principle, a dynamics simulation, such as molecular dynamics (MD) simulation can be time reversible because the classical equations of motion are time reversible. For example, if one runs an MD simulation for a thousand time steps, negates the instantaneous velocities for all particles, and runs for another thousand time steps, one should exactly recover the initial particle positions. However, many simulation software implementations fail to achieve reversibility for two reasons. First, roundoff error during integration leads to a loss of state information; particle positions and velocities at one time step cannot be exactly reconstructed from those at the next time step. Second, lack of associativity of floating point summation leads to a situation where computed forces can depend on various factors that affect order of summation, such that these forces are not uniquely defined by particle positions and force field parameters in an MD simulation.
Large floating point code, scalar or parallel, that ensures exact reversibility for non-trivial dynamics simulation runs is not known to the inventors.